Filters are used in a wide variety of applications. For example, air filters are used to remove dust or other particulates from an air flow stream. Such air filters may be used in a variety of applications to include engine filtration, cabin air filtration, dust collection, and other situations where filtered air is desired. In some instances, filter elements may be used for different filtration applications.
As can be appreciated by those of ordinary skill in the art, an air filter has a limited life span that is determined in large part by the air flow restriction imposed by the filter element. For example, over time as a filter element loads with dust or other particulate, it becomes more and more difficult for air to pass through the filtration medium. The “filter cake” that develops on the filter itself starts to act as a filter and often will increase particle capture efficiency. As a consequence, the filter element and dust loaded thereon becomes more restrictive and prevents the air flow that is desired. For example, an insufficient supply of air may be delivered to an engine for combustion or to heat sink for cooling applications if a filter element is loaded past capacity. As a consequence, the dust loading capacity of a filter is normally closely related to the restriction to air flow imposed by that filter element as it loads with dust.
Equally important are other factors. For example, a filter must be sufficiently tight enough to filter out the undesirable particulates that are anticipated for an application and prevent them from passing through. Thus, a tighter pored, more restrictive media is desired for “filtration efficiency” so to ensure that a high percentage of the undesirable particulates are not allowed to pass through. Even further, the dust holding capacity is also related to the designed change-out interval when an air filter element may be replaced (again the dust holding capacity is likely related to the restriction or pressure drop). Thus, while it may seem logical that you could just simply add additional thicker media to provide for an extended filter life, that is not practical for several reasons. First, the addition of filter media typically increases the initial restriction to air flow which again, as mentioned above, is undesirable. Specifically, increased airflow restriction leads to a quicker change-out interval and starting from a higher restriction value is often undesirable. While increased capacity could be provided by increasing the filter size (e.g. length and diameter), additional space is required. Additionally, original equipment manufacturers and/or existing applications may have a limited filter housing envelope size such that there is only a limited space available for packing in a filter element. In many applications, space is a very valuable commodity and making the air filter system as small as possible is often desirable. Filter envelope size is therefore carefully balanced against the anticipated filter replacement maintenance interval.
For example, one problem in the art is a desire to greatly extend the existing filter change-out interval for air filters housed in auxiliary electrical cabinet filter housings to protect the electrical components on a locomotive from dust particulate. In such an application, the existing filter housing volume is already fixed and the existing filter is changed out at an interval approximately 92 days; and there is a desire to develop a filter that can fit the exact same housing and limited envelope contained therein to last 184 days or about double the life and still maintain a 99 percent average arrestance (efficiency of lifespan). In this application, as can be anticipated, the dust particulate is usually expected to consist of diesel soot and outside particulate. The existing filters used for this locomotive electrical cabinet filter application include the AA-1 and AE-1 filters which are produced and sold by the present assignee, Clark Filter, Inc. These filter elements use a single layer of filter media, which is pleated into a cylindrical filter element. For example, the AA-1 filter element has a height of 12.375 inches, an outer diameter of 8 inches and an inner diameter of 4.75 inches. As such, a replacement filter should have same dimensions or otherwise similar dimensions relative to the limited predetermined space in the filter housing. This filter element has a total dust holding capacity of about 122 grams at the final pressure drop (which has been determined to dictate change interval) of 10 inches of water gauge; with an average arrestance of 99.4 percent.
In light of the foregoing, there is a need and desire to greatly extend and if not approximately double the filter change interval for filter elements, while at the same time maintaining the existing filter envelope size, preferably with minimal or no changes to existing filter housings. The present invention is directed toward particular solutions to the present problems posed in the art; which may also find use in other filtration applications. Indeed, for example, the AE-1 filter of Clark Filter is also used in some applications for engine air filtration in addition to being used as an auxiliary electrical cabinet filter, thus the benefits should not be seen as limited or constricted necessarily to one particular application unless explicitly claimed.